The Panzerkampfwage IV has been described most aptly
as the "workhorse" of the German armoured forces in World War 2; with
continuous development throughout the war as a fighting tank, the
chassis and running gear formed the basis of a number of very important
self propelled weapons.

In 1942 the fighting on the
Eastern Front was making even greater demands on German armoured
resources, as the Soviet Army overcame the setbacks of the successful
German campaign in Russia in 1941.

At this time,
divisional armour consisted predominantly of the Pz Kpfw III and the
Stug III, the later being armed mainly with either the short 7.5 cm gun,
10.5 cm howitzer. The need was for a heavier calibre weapon mounted in
an armured chassis, sufficiently powerful for the demolition of big
city buildings in the street fighting now bein experienced.

In
September 1942 the German Ordnance Dept considered how the problem
could best be overcome as rapidly as possible. The 15 cm heavy infantry
gun, Model 1933 was a readily available weapon, and some limited
experience of it in an armoured role had been gained in 1940 when a
small number of Sig 33's were mounted on the tiny Pz Kpfw I chassis.
The original success of this limited conversion had led, in 1941, to the
decision to build a self propelled version of the Sig 33 on the Pz Kpfw
III chassis. This was like a much heavier version of the original Stug
III, except that the superstructure was very much higher to accept the
greater bulk of the 15 cm howitzer. By the time of the Stalingrad
fighting a first pre-production run of 12 of these vehicles was
available.

By this time, however, the Pz Kpfw IV
was rapidly becoming the most numerous and most important of the German
combat tanks, due to its ability to carry the long 7.5 cm high velocity
gun. In October 1942, the deliberations about the heavy assault vehicle
attracted Hitler's personal attention. He ordered that the Sig 33 gun
be fitted on the Pz Kpfw IV chassis. Due to the urgent requirement for a
street fighting vehicle, the project to fit a 15cm howitzer to the Pz
Kpfw IV chassis was given top priority. The new vehicle, designated
Sturmpanzer IV, was improved in respect of armour protection as a result
of the Stalingrad experience. The Sig 33 was modified, with its barrel
in an armoured sleeve, and the resulting weapon was designated
Sturmhaubitze 43 L/12. A box like armoured superstructure with sloped
sides replaced the original tank superstructure. By any previous
standards it was massively armoure, 100 mm on the front plate, with the
nose of the vehicle given additional armour with a total thickness of 80
mm. The superstructure sides were up to 70 mm thick, and the back was
up to 78 mm thick. The additional weight of the heavy armour took the
total weight of the vehicle up to 30.4 tons as compared to the 22 tons
of the basic Pz Kpfw IV tank. By April 1943, only six months after the
requirements were finalised, the first vehicles were in service on the
Russian front.

Later vehicles were built on
successive production chasis of the Py Kpfw IV and there were thus
Sturmpanzers IV on the Ausf G,H and J chassis. The last production
type, on the J chassis, weighed less, at 28.2 tons, due to the
simplifications introduced on this final type of Pz Kpfw IV chassis.

A
total of 313 Sturmpanzer Ivs were built by 1945 and they served on all
fronts in 1944 - 45 though were initially used on the Russian Front
when first in service in 1943. Lack of close in machine gun protection
proved a serious disadvantage in the close range conditions of street
fighting, so the later vehicles were fitted a ball mount machine gun
high on the front superstructure front. The main armament was itself in
a balltype mantlet with a heavily armoured sleeve. The later
production vehicles had a commander's cupola replacing the plain roof
hatch originally fitted, and a MG 34 in an AA mount was usually fitted
to the cupola.

In the street fighting and close
assault role of the Sturmpanzer IV was highly successful, being
difficult to penetrate except by the most powerful antitank weapons at
close range. The vehicle fully lived up to its name of Brummbar
(Grizzly Bear) which was given to it in 1943. The chassis was very much
overloaded, which led to breakdown and the need for extra careful
maintenance. The Brummbar was in service until the end of the war in
1945, and has remained one of the best remembered due to its massive
appearance.